| 摘要 |
A switched mode converter is disclosed that includes both voltage mode and current mode control. The switched mode converter also includes mode logic for switching between a voltage mode and a current mode. The converter includes current sensing circuitry for sensing the switcher current on the primary side of the transformer and the load current on the secondary side as well as voltage sensing circuitry for sensing the converter output voltage. When the load current is less than a predetermined value, the converter operates in a voltage mode. During the voltage mode, the output voltage of the voltage mode controller is used to control the duty cycle of a pulse width modulation (PWM) controller. When the load current is greater than a predetermined value, the converter operates in a current mode. In a current mode, the primary switcher current is used to control the PWM controller. As such, during a light load in which the converter is voltage controlled, there is no need for a minimum load to stabilize the control loop. In a current-mode, the control loop will have a relatively faster transient response and avoid flux imbalance in push-pull topology. As such, the converter provides the advantages of both known voltage controlled and current controlled switched mode converters. In addition, by the careful arrangement of the locations of a EMC filter, a primary heat sink, a secondary heat sink, a power transformer T1 and other power devices as well as a cooling fan, a smaller EMC filter can be used due to the primary heat sink performing a dual function of thermal management and additionally providing EMC shielding to prevent the noise, for example, the noise generated by the transformer, from reaching the filter. In addition, the primary heat sink is configured to face the air flow while the secondary heat sink is placed close to the fan with its fin direction the same as the direction of the air flow. As such, both the primary and the secondary heat sink get maximum air flow, allowing smaller heat sinks to be used in order to provide a reliable and cost-effective switched mode converter.
|
